1. Field of the Invention
The present invention relates to a scan-type radar provided on a vehicle and, more particularly, to a scan-type radar apparatus which detects an object existing in a lane in which the radar equipped vehicle is moving.
2. Description of the Related Art
Conventionally, a radar apparatus for a vehicle which detects an object anterior to the radar equipped vehicle is known, for example, in Japanese Laid-open Patent Application No.6-150195. This conventional radar apparatus comprises a radar which is capable of detecting the positions and orientations of a plurality of objects existing in a wide area anterior to the radar equipped vehicle. According to such a radar apparatus, a relative position of each of the objects existing in the detectable range with respect to the radar equipped vehicle can be detected.
In order to utilize the results of the radar apparatus for the control of a vehicle operation, it is required to accurately determine whether the objects detected by the radar apparatus exist in the lane in which the radar equipped vehicle is moving. Hereinafter, the lane in which the radar equipped vehicle is moving may be referred to as a radar equipped vehicle moving lane. When the radar equipped vehicle is moving in a straight line, it can be assumed that the radar equipped vehicle moving lane extends forwardly of the radar equipped vehicle and has a predetermined lane width. Accordingly, in such a case, an area corresponding to the radar equipped vehicle moving lane can be accurately recognized within the detectable range of the radar apparatus. When the radar equipped vehicle moves along a curve, it can be assumed that the radar equipped vehicle moving lane extends forwardly of the radar equipped vehicle in accordance with the radius of curvature of the curve. Accordingly, if the radius of curvature is known, the area corresponding to the radar equipped vehicle moving lane can be recognized in the detectable range of the radar apparatus.
In the above-mentioned conventional radar apparatus having a wide detectable range in the anterior of the radar equipped vehicle, an object existing in the radar equipped vehicle moving lane can be detected in the detectable range whether the radar equipped vehicle is moving on a straight road or a curved road. The radius of curvature of a road on which the radar equipped vehicle is moving can be assumed based on an operating condition of the vehicle such as a yaw rate w.sub.y. Accordingly, in the above-mentioned conventional apparatus, a lane area of the radar equipped vehicle can be recognized in response to the operating condition of the vehicle. Thus, an object which is not in the radar equipped vehicle moving lane can be distinguished from an object in the radar equipped vehicle moving lane, when the object is detected by the radar apparatus, by determining whether or not the object is in the recognized lane area.
If an object detected by the radar apparatus is a vehicle moving anterior to the radar equipped vehicle, the object vehicle enters a curve before the radar equipped vehicle enters the curve. Accordingly, in the method in which the lane area is determined by assuming the radius of curvature based on the operating condition, an object in the radar equipped vehicle moving lane may be erroneously recognized as one which is not in the radar equipped vehicle moving lane during the period from the time when the object, such as a vehicle moving anterior to the radar equipped vehicle, enters a curve to the time when the radar equipped vehicle enters the curve.
The above-mentioned problem may be eliminated by setting a lane area having a greater width in the detectable range. Alternatively, the problem can be eliminated by detecting the radius of curvature of the road extending in an anterior direction of the radar equipped vehicle by using an image recognizing apparatus. However, the former method may decrease the accuracy of discrimination between objects existing and not existing in the radar equipped vehicle moving lane. The later method may increase manufacturing cost of the radar apparatus. As mentioned above, in the conventional radar apparatus, it is difficult to provide a radar detection function which accurately discriminate between an object existing in the radar equipped vehicle moving lane and an object which is not existent in the radar equipped vehicle moving lane, at a low manufacturing cost.